1. Field of the Invention
This invention relates to an improvement on a buried-type semiconductor laser device to be used as a light source in an optical telecommunication system.
2. Prior Art
A semiconductor laser device to be used as a light source in an optical telecommunication system is required to have various functional features such as a high output power and a low threshold current, and a high speed modulation capability.
A buried-type semiconductor laser device (having a BH structure) is known to meet such requirements.
FIG. 2 of the accompanying drawings illustrates a typical known buried-type semiconductor laser device.
Referring to FIG. 2, the buried-type semiconductor laser device 14 comprises an n-InP semiconductor substrate 15, on which an n-InP buffer layer 16, a nondoped GaInAsP active layer 17 (having an energy band gap wavelength of 1.3 .mu.m), InP clad layers 18 and 19 and a GaInAs contact layer 20 are sequentially formed by means of an epitaxial growth technique such as the MOCVD method to bring forth a multilayer structure.
Additionally, p-InP current blocking layers 21 and n-InP current blocking layers 22 extends from the respective upper edges of the clad layer 18 to cover the etched areas of the buffer layer 16 and then grooves 23 are cut through the current blocking layers 21 and 22, the clad layer 19 and the contact layer 20 in order to reduce the device capacity. The grooves 23 and part of the segmented contact layer are covered by an SiO.sub.2 insulating film 24.
3. Problem to be Solved by the Invention
A buried-type semiconductor laser device 14 having a configuration as illustrated in FIG. 2 is subject to internal stresses (distortions) particularly in the active layer 17 which is particularly remarkable at high temperature due to the significant difference in the thermal expansion coefficient between and the close physical proximity of the insulating films 24 covering the surface of the grooves 23 and the active layer 17.
A semiconductor laser device 14 which is subject to such distortions cannot reliably operate for a long period of time.
4. Object of the Invention
In view of the above identified technological problem, it is therefore an object of the present invention to provide a buried-type semiconductor laser device that operates stably and reliably at high temperature for a prolonged period of time.